This invention relates to an electronic shutter control device used for a still video camera, etc, and a method for controlling the same.
So-called electronic shutter using a CCD which is a solid imaging device is generally used in a still video camera, etc. In a conventional shutter driving device in the still video camera, readout of an image signal representing an electric charge accumulated in the CCD (hereinafter referred to as an electric charge signal) to a vertical transfer section is synchronized with the vertical synchronous signal in an image processing circuit (for example, refer to "Television Technology", Aug. 1987, pp. 37-39).
This is necessary because a vertical transfer section in the CCD is provided to receive an electric charge signal from a photoelectric converter section in the CCD, the electric charge signal is read out as a TV signal and image recording is made at predetermined intervals, i.e., fundamentally a movie.
In this prior art shutter control device, since said reading out of the electric charge signal to the vertical transfer section, i.e., the shutter closure is synchronized with a video vertical synchronous signal, timing of the shutter open timing is restrictedly determined at a timing preceding to a desired exposure time from the vertical synchronous timing so as to obtain a proper exposure. Additionally, since shutter release is made irrespective of the vertical synchronous timing, time irregularity may be observed from any release timing to the shutter open timing. Moreover, since the exposure time is obtained in advance of the shutter release on the basis of the light measurement before the shutter release, i.e., the exposure time is not based on the light measurement during the exposure, i.e., the real time photometry, incorrect exposure happens to occur especially at the flash photographing.
Thus, the photometrical precision improvement was limited because the real time photometry could not be realized in the prior art techniques.
Another known method consists in driving an electronic shutter synchronizing with a release switch (for example, refer to the Japanese Laid-Open Patent Publication No. 60-52173), but no consideration to obtain shutter open timing anytime, is given.